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In situ osmometry: validation and effect of sample collection technique
Moneisha Gokhale1, Ulrike Stahl, Isabelle Jalbert
1School of Optometry and Vision Science, The University of New South Wales, Sydney, New South Wales, Australia. m.gokhale@unsw.edu.au
Summary
Tear film osmolarity measurements using in situ and vapor pressure osmometers showed moderate correlation. On-eye measurements were higher than collected samples, emphasizing the importance of direct measurement for accurate tear osmolarity assessment.
Area of Science:
- Ophthalmology
- Biomedical Engineering
Background:
- Tear film osmolarity is a key indicator of ocular surface health.
- Accurate measurement of tear film osmolarity is crucial for diagnosing and managing dry eye disease.
- Existing methods for tear osmolarity measurement have varying degrees of accuracy and repeatability.
Purpose of the Study:
- To compare tear film osmolarity measurements obtained with an in situ osmometer versus a vapor pressure osmometer.
- To evaluate the repeatability of in situ osmometer measurements.
- To assess the impact of sample collection techniques on tear film osmolarity readings.
Main Methods:
- Tear film osmolarity was measured in 52 healthy participants using both in situ and vapor pressure osmometers.
- Repeatability was assessed by performing duplicate on-eye measurements with the in situ osmometer in a subset of 20 participants.
- The effect of sample collection was evaluated by comparing on-eye measurements with measurements from collected tear samples (3 μL) using both instruments.
Main Results:
- Mean tear film osmolarity showed moderate correlation between the in situ (299.2 mOsmol/L) and vapor pressure (298.4 mmol/kg) osmometers (r = 0.5).
- On-eye tear osmolarity measurements were consistently higher (5.0 mOsmol/L) than those from collected tear samples, with good correlation (r = 0.65).
- The in situ osmometer demonstrated good repeatability with a coefficient of repeatability of 9.4 mOsmol/L (r = 0.8).
Conclusions:
- Tear film osmolarity measurement is influenced by sample collection technique, with on-eye measurements yielding higher values.
- Direct on-eye measurement is critical for accurate tear film osmolarity assessment.
- The in situ osmometer provides repeatable measurements for on-eye tear film osmolarity.
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